Bimetal thermostats are well known to the prior art and, typically, such thermostats are designed to be deformed at predetermined temperatures. Upon deformation, the bimetal thermostat will move whereby to actuate a mechanical or electrical impulse. Conventional bimetals are used to yield a deflection of the structure with a change in temperature by utilizing the differences in the coefficients of expansion of two alloys that are metallurgically bonded along a common interface. As can be appreciated, these bimetal materials deflect throughout a given temperature range and hence it is necessary to label them so that the consumer can know their characteristics.
In the manufacture of ferrous metal bimetals according to the prior art, it has been conventional to temper the bimetal piece and relieve residual stress by heating it in an oxidizing atmosphere after the two sections of the bimetal have been fabricated and shaped into a final usable form. One of the more successful tempering operations has been to heat the bimetal in a salt bath at 600 degrees F. for 60 to 90 minutes. During this heat treatment, a dark purple to dark blue-hued ferrous oxide coating develops on the surface of the bimetal. This coloration varies according to the thickness of the oxide coating that is formed. The indicia which were marked previously are difficult to read and the product is less appealing, cosmetically.